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arXiv · 2401.07508

Phase diagram of a square lattice model of XY Spins with direction-dependent interactions

Fan Zhang·Wenan Guo·Ribhu K. Kaul
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Abstract

We study a generalization of the well-known classical two-dimensional square lattice compass model of XY spins (sometimes referred to as the 90$^\circ$ compass model), which interpolates between the XY model and the compass model. Our model possesses the combined $C_4$ lattice and spin rotation symmetry of the compass model but is free of its fine-tuned subsystem symmetries. Using both field theoretic arguments and Monte Carlo simulations, we find that our model possesses a line of critical points with continuously varying exponents of the Ashkin-Teller type terminating at the four-state Potts point. Further, our Monte Carlo study uncovers that beyond the four-state Potts point, the line of phase transition is connected to the lattice-nematic Ising phase transition in the square lattice compass model through a region of first-order transitions.

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Fan Zhang, Wenan Guo, Ribhu K. Kaul. 2024-01-15. Phase diagram of a square lattice model of XY Spins with direction-dependent interactions. https://doi.org/10.1103/physrevb.109.195131

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